Made $alert variable more extensible through use of apply_filters() function

This allows the html markup to be altered to developer's liking, as well as the actual alert message text, including CSS class names that need to be modified or added to.
Added else condition to set $first name and $last name to nothing

Fixes 2 Undefined variable notices and "cannot modify header information" warning
Move settings around
Introduced edd_single_price_option_mode() for #688
Added new Single Price Option Mode checkbox for #688
Merge pull request #775 from fxbenard/master

[i18n] > update french.po.mo and edd.pot
Removed unnecessary if check in templates. #541
Merge branch 'master' of github.com:pippinsplugins/Easy-Digital-Downloads
Added new edd_payment_view_details hook
Added new edd_payment_view_details hook
Added new edd_payments_table_views filter
Added new edd_payments_table_columns filter
Added new edd_payments_table_column filter
Made payments list table bulk actions extensible.
Moved edd_payment_view_details above close button
Merge pull request #776 from Geczy/settings-file-organization

Move setting files around
Refactored edd-ajax.js for #688
Refactored edd-ajax.js for #688
Refactored edd_ajax_add_to_cart() for #688
Refactored edd_item_in_cart() for #688